System for evaluation of irregularities on large surfaces



Dec. 15, 1970 (5, w COOK 3,546,948

SYSTEM FOR EVALUATION OF IRREGULARITIES ON LARGE SURFACES Original FiledDec. 27, 1966 2 Sheets-Sheet 1 f mi 90 v jj-qs George W. Cook INVENTORDec. 15, 1970 w, COOK 3,546,948

' SYSTEMI'OR EVALUATION OF IRREGULARITIES ON LARGE SURFACES OriginalFiled Dec. 27, 1966 2 Sheets-Sheet JNVEN'TOR.

George W. Cook I United States Patent 3,546,948 SYSTEM FOR EVALUATION OFIRREGULARITIES 0N LARGE SURFACES George W. Cook, McLean, Va., assignorto Thiokol Chemical Corporation, Bristol, Pa., a corporation of DelawareOriginal application Dec. 27, 1966, Ser. No. 605,009, now Patent No.3,475,954, dated Nov. 4, 1969. Divided and this application June 23,1969, Ser. No. 851,517

Int. Cl. Gtllp 3/26; G01c 19/14 US. Cl. 73-505 5 Claims ABSTRACT OF THEDISCLOSURE A system for determining the bumpiness of large sur faces,such as the surfaces of highways or air fields, the system including awheeled vehicle carrying an angular velocity meter which measures thepitching rate of the vehicle and provides an electrical outputrepresenting the rate of change of slope of the surface, the meterhaving a pair of tubular loops containing hydraulic fluid pumped throughthe loops at the same speed but in opposite directions, and adifferential pressure device interconnecting the loops and sensitive toangular rotation of the loops.

This application is a division of pending application Ser. No. 605,009,filed Dec. 27, 1966, now Pat. 'No. 3,475,954.

The present invention relates to a system for quantitative evaluation ofthe unevenness or irregularities on large surfaces, and moreparticularly to a system for checking the surface of highways or thelike for determining whether such surfaces possess irregularities whichare excessive, and marking such irregular surface for correction orrepair.

The first tangible evidence of distress in -a roadway or other surfaceis a structural deformation producing an irregularity on the surface. Ifsuch a defect is located and repaired promptly, the cost is relativelyminor. However, if it is not tended to until after the surface starts tobreak up, which deterioration could take place in a short time dependingon the nature and amount of the road traflic, the repair operationbecomes major and costly. Perhaps even greater importance attaches tosuch defects in the surfaces of high speed jet airfields and railwaysbecause of the possibility of also inducing harmful vibrations and otheradverse effects in the vehicles travelling over such surfaces. With theadvent of supersonic jets and ultra high speed trains and the thousandsof miles of roads, railways and airfields already in existence andplanned, examination of these surfaces by manual means, such as the rodand level, is already an impossible task. A considerable amount ofeifort has been expended in the design and development of machines whichcan be run over road surfaces to obtain automatically informationconcerning irregularities on the surfaces. However, the goal has been toduplicate in large measure the work of a surveying team obtaining databy means of a rod and level with the result that the work done on suchmachines has been to produce a machine which obtained data relating tothe profile of the roadway, i.e., measurement of elevation at spacedpoints along the length of the roadway. But applicant has observed thatinformation in the form of elevation or profile data is not usefuldirectly for the reason that the meaningful measure of unevenness orbumpiness in a surface derives from the changes in a slope on thatsurface; in other words, a bump cannot exist without a change in slope,and elevation or profile information must be differentiated twice withrespect to the distance travelled in order to arrive at the necessarydata form. Put another way, a change in slope of a line or surface ischaracterized by the physical quantity known as curvature" and thecurvature of a line is a direct measure of the rate-of-change of slopewith respect to the distance travelled along the line or curve. A systemor technique wherein curvature is measured directly would be usefulsince then no basic conversion operations are required to evaluate theunevenness of the surface under examination.

The fundamental definition of curvature at a point on any line or curveis:

AT dT K :3 ZE E where:

K is the curvature sis the segment of the curve T is the angle subtendedby the segment The tangential velocity along any curve may be defined asthe time-rate-of-change of distance along the curve which, in turn, maybe defined as the radius of curvature times the time-rate-of-change ofthe angle subtended by the segment of the curved traversed. Thus,algebraically:

'Where:

V, is the tangential velocity R is the radius of curvature, and s and Tare as hereinbefore defined By definition, time-rate-of-change of theangle is the angular velocity or dT/dt=w from which Equation 2 may berewritten as:

Since curvature is the reciprocal of the radius of curvature:

which is the fundamental definition of curvature.

Thus, Equation 4 is seen as a true representation of the curvature andit is clear that the angular velocity is a direct measure of thecurvature provided that the tangential velocity is finite and heldconstant. Also, it is seen that the relationship is linear and that nodata processing is required to obtain the necessary curvature quantity.

It is therefore an object of the present invention to provide means fordirectly measuring the curvature of a surface under examination fordetermining the irregularities or unevenness thereof.

Another object is the provision of means which sense the unevenness of asurface and record information thereof for analysis and evaluation.

A further object is to provide means to ascertain excessiveirregularities on a surface and mark the same.

Still another object is the provision of means for indicating relativechanges in heading, which means is nongyroscopic and of ruggedconstruction.

In accordance with the invention, there is provided a system comprisinga vehicle having an angular velocity meter mounted thereon and rollers'which follow the profile of the surface under examination, the metermeasuring the pitching rate of the vehicle while travelling over thesurface and providing an output representative of the rate of change ofslope of the surface.

The exact nature of this invention as well as other objects, featuresand advantages thereof will become better understood by reference to thefollowing detailed description considered in connection with theaccompanying drawings in which:

FIG. 1 is a schematic representation of a sensor vehicle or carriagewhich may be employed in accordance with the invention;

FIG. 2 is a schematic showing of one embodiment of the vehicle of FIG. 1adapted to be propelled by a powered land vehicle;

FIG. 3 is a schematic representation of the means for indicatingrelative changes in heading;

FIG. 4 is a schematic representation, in perspective, of a thin disk orpancake of rotating fluid;

FIG. 4a is a showing of a portion of FIG. 4, on an enlarged scale andillustrating the forces acting on a differential element of fluid; and

FIG. 5 is a perspective view of a more practical arrangement of theindicating means of FIG. 3.

Referring now to the drawings, wherein like reference charactersdesignate like or corresponding parts, there is shown in FIG. 1, inschematic form, a sensor carriage or vehicle designated generally byreference numeral and comprising a frame or chassis 11 mounted on a pairof rollers or wheels 12 and supporting angular velocity measuring meansor meter 13, wheels 12 being adapted to follow the profile of a surface14. The angular velocity measuring means is fixed to chassis 11 and isadapted to measure directly the pitching rate of the chassis and deliveran output voltage e which may be applied by suitable leads and switchmeans S S to data recording means 15 or to servo means 16, or both, asdesired.

In FIG. 2 there is shown, in schematic, a powered land vehicledesignated generally by reference numeral 17 and comprising a chassis orframe 18 supported on a pair of steerable wheels 19 and a single drivenwheel 21 adapted to be driven by power means 22. Pivotally connected tothe chassis 18, as at 23, is a towing means 24, generally in the form ofa bellcrank and having a vertical portion 25 and a generally horizontaltowbar portion 26 which may take the form of a Wishbone yoke. Portion 26is pivotally connected, as at 27, to a pair of connectors 27 fixed tothe sides of chassis 11, the pivot connections 27 providing a generallyhorizontal pivot axis disposed below a line through the centers ofrotation of wheels 12.

Provision is made for swinging towing means 24 in one direction to liftwheels 12 off surface. 14 and in the other direction to force the wheelsagainst the surface. To this end there is provided an adjustablebellcrank 28 having a horizontal member 29 and a vertical member 31,member 29 being attached by a flexible connection 32 to portion 26 ofthe towing means and member 31 being connected to portion 25 of thetowing means by a tension spring 33. It is to be understood thatbellcrank 28 may be locked in any desired position of adjustment by anyconventional means (not shown) and may be adjusted to positions in whichflexible connection 32 is slackened and spring 33 is stressed and Wheels12 are pressed against surface 14 with a force of about three to seventimes their weight to reduce bouncing. Wheels 12 are provided withsemicompliant tires (not shown) to absorb severe road shocks andadditional vibration damping may be provided by the use of dash potmeans 34 or the like. Pivotal movement of chassis 11 relative to thetowing means is limited by a U-shaped strap 35 secured to an extension11' of chassis 11 and extending over portion 26 of the towing means forengagement thereby when the towing means is 4 lifted; vibration dampingtherebetween being provided by means of a dash pot 36 or the likeconnected between chassis 11 and an extension 26' of portion 26.

The angular velocity measuring means 13 carried by the chassis 11 may beof any form which reads out the angular velocity or pitching rate of thechassis. For example, the widely-used rate-gyro, which is essentially asingle degree of freedom device providing an output signal proportionalto the velocity of rotation of the device about its input axis, could beused for this purpose. Thus, fixed in proper orientation to the frame ofa vehicle adapted to travel over a surface having changes in slope therate gyroscope can be made to read out directly the pitching rate of thevehicle induced by the changes in slope during constant speed travel ofthe vehicle.

However, as a practical matter, the rate gyroscope is not suflicientlyrugged to withstand shocks imparted to the sensor vehicle by holes andother very rough spots in the road surface. It is therefore preferred tosubstitute for the rate-gyro an hydraulic angular velocity indicator,hereinafter referred to as HAVI, which serves to indicate relativechanges in heading in any plane but is not a gyroscope, there being nogimbal rings or critical bearings such as those characteristic ofgyroscopic installations, and is of sufficiently rugged construction toaccommodate road shocks.

The fundamental principle of operation of the HAVI is based on theCoriolis effect which has to do with the behavior of particles followingcurvilinear paths on a rotating reference. In its broadest aspects, theHAVI comprises two counterrotating masses of fluid having angularvelocities of opposite values. Turning now to FIG. 3, the HAVI 13 maytake the form of a pair of identical circular loops 37, 38 mounted on asupporting platform 39. Each loop is provided with a positivedisplacement pump, the two identical pumps 41 and 42 beinginterconnected for rotation at the same speed from a single motor M andhaving equal volumetric deliveries for pumping a mass of fluid fillingloop 37 in a direction opposite to that of an equal mass of fluidfilling loop 38. Diametrically opposite the pumps is a differentialpressure sensor 43 containing a pair of conventional differentialpressure gages 44 which are tapped into the loops 37, 38. Since theloops and pumps are identical, the angular velocities of the fluidmasses in the loops induced by the pumping are equal in magnitude butopposite in direction and may be designated 9 and Q for loops 37 and 38respectively. As the particles of fluid rotate due to the pumping,centripetal acceleration forces (1 and a are directed toward the loopcenters 0 and 0 When the platform 39 is stationary, these accelerationforces are equal and have a common value designated a thus:

where:

R and R are the outer and inner radii of either loop (2,, is the angularvelocity of the fiuid particles due to pumping.

However, if now the platform 39 is rotated in the direction of the arrowat an angular rate w,,, the spatial velocities of the fluid in the loopsare no longer equal since in the one case the rotation of the platformis in the same direction as the rotation of the fluid in loop 37 whilein the case of loop 38 it is against the direction of fluid rotation.The spatial angular velocity of the fluid particles in loop 37 is then:

from which the centripetal acceleration forces may be evaluated as:

from which it is apparent that the angular rate of turn of the platformcan be determined in terms of sense and magnitude by suitable andappropriate means which measure and evaluate the difference in theacceleration forces. It is further apparent that if thi sdifference isintegrated as a function of time, any change in the angular position ofthe platform can be measured and evaluated.

The tangential velocity of the field in either loop is:

V.=( Z )s2., 11

and Equation may now be written as:

a a =4V w In classical mechanics the Coriolis acceleration is expressedas 2Vw. The result shown in the right-hand portion of Equation 12 isseen as twice the Coriolis acceleration.

Considering further the forces acting on the particles of a rotatingfluid mass, attention is directed to FIG. 4 which illustrates a rotatingdisk or pancake 45 of fluid having a center 0, a radius R mass density pand an angular velocity 9. A differential element of fluid at radius 1:,having an area dA and a radial thickness dlr, has acting on it anoutwardly directed pressure P and an inwardly directed pressure P+dP(FIG. 4a) and the restraining force F acting on the element is:

F dPdA 13 where:

dP is the net pressure on the element dA is the area on which pressuredP acts Classically, the force F is also:

. Fzma Where m=the mass of the fluid in the differential element a zthecentripetal acceleration acting on the element Since the volume of theelement is dA dr, the mass may be expressed as:

m= dAdr and the centripetal acceleration as:

from which Equation 14 may be rewritten as:

F: dAdr) (rQ )=pS2 rdrdA (15) Equating Equations (13) and (15) gives:

dPdA= Q rdrdA 0r dP= Q rdr (16) which is the differential equation forthe centrifugal reaction pressure in the rotating fluid disk 45 fromwhich the pressure at the edge of the disk may be found:

Where the configuration of the rotating fluid is a ring or loop havingan outer radius R and an inner radius R, the pressure at the outside ofthe ring is:

JR: 2 is) from which it is clear that the centrifugal reaction pressuredeveloped in a confined rotating fluid body is a function of the massdensity of the fluid, its angular velocity and a design constant.

Returning to FIG. 3 and referring again to Equations 6, 7 and 18 thecentrifugal reaction pressure in each loop can be determined when thetrue spatial angular velocity is used in place of the general term 9:

The difference or differential pressure AP, is:

AP =P.-P.=p(R.-R. 9 0)] a quantity which can be measured by thedifferential pressure sensor 43.

Employing the equality in Equation 11, Equation 21 may be rewritten as:

A13:10 (RO R1) r p) from which it is seen that the differential pressureis twice the Coriolis acceleration multiplied by a design constantinvolving the mass density of the fluid and a radial dimension and istherefore directly proportional to such acceleration.

Furthermore, comparing Equations 12 and 22 the differential pressure isseen as a directly proportional measure of the difference between thecentripetal acceleration forces.

Turning now to FIG. 5, there is shown a more practical arrangement ofthe HAVI, designated generally by reference numeral 13" in whichidentical loops of tubing 37, 38, toroidal in form, are mounted on aplatform 39' adjacent each other and have a common central axis ZZ forrendering the HAVI immune to extraneous and spurious forces. Loops 37and 38' have associated therewith identical pumps 41' and 42'respectively which are geared together as at 40' for operation in unisonby an electric motor M. Diametrically opposite the pumps is adifferential pressure sensor means 43' containing a pair of pressuregages (not shown), which are in communication with the loops 37' and 38and a pressure transducer means (not shown) operatively connected to thepressure gages for delivering an electrical voltage output erepresentative of the differential pressure.

The pressure P across each pump 41' and 42' is made up of a component atthe positive pressure or force side of the pump and a component at thenegative pressure or suction side of the pump, the former having a valueof P /Z and the latter a Value of P 2, assuming the pump to have zerolength. Progressing around the associated loop, the pump pressure fallsuniformly and passes through zero halfway around, or diametricallyopposite the pump, at the point Where the associated pressure gage istapped into the loop. Thus, the pressure at each gage point is zero withrespect to its associated pump and the differential pressure between thetwo gage points due to the pumping effort is O0= 0.

Referring to Equations 19 and 20, it will be appreciated that the changein pressure in each loop 37' and 38 due to the angular velocity w of theplatform 39' about the Z-Z axis is additive in loop 37' and subtractivein loop 38' and the differential pressure between the loops is thusequal to twice the change in pressure in each loop and is the usefuloutput signal of the HAVI.

The effect of angular acceleration about the ZZ axis is a pressurechange across each pump 41 and 42, the component of such pressure changeon one side of a pump being of equal magnitude but opposite value to thepressure change component on the other side of the pump with the resultthat the effect is self-cancelling in each loop. In this case thepressure at each gage point is zero and the differential pressure isO=0.

In the case where the loops are subjected to linear acceleration alongthe ZZ axis, there is no pressure change around the loops and thepressure due to such acceleration at the pumps and gage points is zeroand the differential pressure is 00=O. However, linearly acceleratingthe loops along the XX axis results in a pressure build up in thetrailing half of the loop and a corresponding reduction in pressure inthe leading half of the loop with zero pressure at the pumps and gagepoints and again the differential pressure is 00=0. Linear accelerationalong the YY axis similarly increases and decreases the pressure in theloops but now the maxima and minima occur at the pumps and the gagepoints and the differential pressure developed equates to zero.

Rotation of the loops about the X-X axis induces equal increases inpressure in the loop halves on each side of the axis, the maximaoccurring at the pumps and the gage points and the differential pressureequating to zero. With rotation about the YY axis, the maxima occurbetween the pumps and the gage points, the pressure at the pumps andgage points being zero and the differential pressure being 00:0.

From the foregoing, it is clear that the HAVI can be subjected toaccelerations and motions about the several axes simultaneously and thatthe differential pressure developed will be proportional only to theangular velocity of the HAVI about the Z-Z axis, that is, the centralaxis of the loops. This freedom of sensitivity from all other motions isan important advantageous feature of the HAVI. Also, the fluid particlesin the loops are forced to follow paths which they would not follow wereit not for the constraint of the circular conduits, and the fluidpressures at the respective gage points serve as direct measures ofthese constraining forces. With the fluid in the loops incounter-rotation, an hydraulic force balance, much like the electricalequivalent known as the Wheatstone Bridge, is established, the hydraulicbridge being unbalanced by rotation of the loops about their commoncentral axis and the magnitude of the unbalanced forces showing up as adifferential pressure which is proportional to four times the product ofthe fluid velocity and the angular velocity of rotation of the loops.The unbalanced forces are also a direct measure of the changes incentripetal forces acting on the fluid particles. The HAVI can thereforebe used as a basic sensor for a variety of systems and possesses theadvantage of the elimination of the need for gimbals and criticalbearings.

In its application to the sensor vehicle of FIG. 1, the HAVI 13"replaces the angular velocity measuring means 13 and is rigidly mountedon the vehicle with the central axis (ZZ axis in FIG. 5) of the loopslocated coincident with, or close and parallel to, the pivot axis 27 ofthe vehicle.

In order to simplify the speed control of the land vehicle 17, and ofthe sensor vehicle 10, drive wheel 21 may be driven by an electric motorcontained in the power means 22 which means also contains a speedcontrol for the motor, batteries to drive the motor and a gasolineengine and a generator for charging the batteries; power for motor M ofthe HAVI 13" being taken from the batteries. Additionally, a tachometergenerator may be coupled to one of the sensor wheels 12 and its outputvoltage applied to a reciprocal modulator for varying a variableamplitude coefiicient of the output voltage e from the meter 13, or efrom the HAVI 13", inversely with respect to the tangential velocity ofthe wheel, thus tending to keep the product of the amplitude coefficientand vehicle velocity constant over a limited range and thereby reducingthe requirement that the speed of the land vehicle be maintainedconstant. If desired, vehicle 17 may be provided with a road sweeper 46for the purpose of clearing the surface ahead of any debris in the pathof the vehicles, conventional means 47 serving to lift the sweeper.

The output voltage e of the meter 13, or c of the HAVI 13", may beapplied to the data recording means 15 which may be any one of theseveral types available, the simplest type being a direct-writinggraphic strip-chart recorder on which are recorded: (1) the net outputsignal of the angular velocity meter (which indicates the bumpinessdirectly), (2) the distance travelled (which conveniently may beindicated by means coupled to one of the sensor wheels for generating apip marker on the chart for each revolution of the wheel) and (3) timemarkers on the chart for verifying the running speed of the landvehicle.

The output e or e,,' may also be connected to servo means 16 which isthen actuated whenever the output exceeds a predetermined value which isindicative of extreme unevenness or bumpiness of the roadway. Whenactuated, servo means 16 controls the flow of paint or other markingmaterial from a container 48 through a pipe 49 for marking the roadsurface. Such marks indicate points where, upon closer examination,maintenance work is required or desired.

In operation, the sensor vehicle 10 is moved at a predetermined speedwith Wheels 12 in contact with surface 14 and chassis 11 pivotingrelative to towbar 26 as the wheels travel over irregularities in thesurface. The signals from angular velocity meter 13, or from the HAVI13", are fed to the data recording means 15 or servo means 16, or both,as desired. Vehicle 10 may be moved over the surface at relatively highspeeds so that a relatively long length of surface may be examined orchecked in a short time. For examination of wider surfaces, such aslanding fields for aircraft, several sensor vehicles may be positionedalongside each other and several lines then checked simultaneously.

There has thus been provided means for directly measuring the unevennessor irregularities in a surface and accumulating data relative theretoand/or marking excessive irregularities. Obviously many modificationsand variations of the present invention are possible in light of theabove teachings. It is therefore to be understood that the invention maybe practiced otherwise than as specifically described.

What is claimed is:

1. Hydraulic angular velocity indicating means comprising, incombination:

a pair of conduits of like configuration and dimensions forming closedloops, mounted on a member whose angular velocity is to be sensed withthe axis about which rotation is to be sensed extending perpendicular toand through said loops;

equal masses of fluid filling said conduits;

means connected to the conduits for moving said masses of fluid each inits respective conduit at equal speeds but in opposite directions; and

differential pressure means interconnecting said conduits for measuringthe difference between the pressures of said masses of fluid.

2. The combination of claim 1 wherein said conduits are circular, andsaid means for moving the masses of fluid comprise a pair of identicalpumps, one each associated with a conduit respectively, said pumps beinginterconnected for operation in unison, and said differential pressuremeans interconnecting points on the conduits most distant from thepumps.

3. The combination of claim 2 wherein each of said conduits has theshape of a torus, and the conduits are disposed in parallelism and havea common central axis.

4. The combination of claim 2 wherein said conduits are disposedcoaxially adjacent each other, and said pumps are geared together foroperation by a single motor.

5. The combination of claim 2 wherein said conduits are coaxial, andsaid conduits and pumps are closely adjacent each other, and saiddifferential pressure means are 5 diametrically opposite the pumps.

References Cited UNITED STATES PATENTS 3,372,596 3/1968 Keller 73-505JAMES J. GILL, Primary Examiner

